Making Acetal leadscrew nuts the easy way

[Evan]

A standard acme plastic lead screw nut from Nook 1/2 x 10 is rated at 625 lbs static and dynamic load. That should be enough.

[squirrel]

If you could do that with pot metal the Atlas guys would make you a super hero.

[alanganes]

I'm sensing a mad rush of acetal nut-making brewing for all manner of machine tools. Very nice work, Evan. And thanks for passing along such clear and thorough instructions. Lots of uses for this sort of thing for folks like us.

Very cool.

[darryl]

I've used that method several times myself, mostly just experimenting. After polishing the screw with green scrubbie (could have used purple ) I coated the screw with Top Cote, let dry, coat again, let dry. I did NOT wipe it after coating, figuring that the slippery powder would remain and get pressed into the plastic. It seemed that there was a reduction in friction, but I didn't do any long term testing to see if it remained.

Now I want to make a nut this way again, but dust the screw with graphite powder before forming the nut onto it. I doubt that I will do a long term test on that, but I would leave this experiment on my computer desk so I could play with it lots.

Evan has used a round piece of acetal- you could just as easily use rectangular pieces and contain it within a piece of channel once it's formed. Actually, you could form it in the vise with the channel in place, and the final result could be something easier to mount. I'd probably make the channel in such a way that some mounting tabs are already prepared on them.

Just some more ideas.

[Evan]

I ground the screw to use it for chasing the threads like this:



This worked perfectly if you want it still slightly tight. Freezing or cooling it first should produce a perfect smooth fit. If you are using a screw that is from the machine then grinding just a small notch at one end should be sufficient although it will take more passes.

I then decided to crack it open to see what the threads look like. It took quite a bit of force to break it open. I wasn't expecting the threads to look this good.



Some more pictures later on this topic.

[DICKEYBIRD]

Evan has used a round piece of acetal- you could just as easily use rectangular pieces and contain it within a piece of channel once it's formed. Actually, you could form it in the vise with the channel in place, and the final result could be something easier to mount.

Yabbut you wouldn't be able to guarantee concentricity without turning the O.D. in a lathe.

Methinks the heat forming process allows the leadscrew to drift around a bit making the lathe op a must unless one could come up with a jig to hold everything in perfect alignment while heating and compressing, no?

[Evan]

You must turn it on the lathe afterward since it isn't round after the heat forming step. The kerf closes up and the result is an ovoid.

[The Artful Bodger]

Evan, I tried making a nut and it worked perfectly. I might have got my screw hotter than necessary and there was a good flow out into the kerf such that the nut now appears to be well welded in one.

[JRouche]

Outstanding work Evan!!!! At first I was a lil baffled till I saw the last pics. I was thinking, how in the heck did the cut line get bonded all the way out to the OD of the cylinder. Then that last pics shows it didnt. And thats a good thing cause I didnt see anyway for the OD to get bonded unless the heat was a whole lot more.

I do see a small section that appears to have gotten hot and pulled a bit off the opposite side? Or is that a picture thing and its still the cut face. Almost looks like I can see cut lines on the section that looks like it was lifted..

Anyway... Really great work. I for one love all the great ideas. Reminded me of my ol biker buddy from years ago. He was one of the most resourceful folks I have ever met. Till I came to HSM... JR

[dp]

I then decided to crack it open to see what the threads look like. It took quite a bit of force to break it open. I wasn't expecting the threads to look this good.

It's really quite amazing, actually. I'd never have guess the threads would be fully formed and the clamshells would be welded. There are surely possibilities - heat formed worm gears, for example.

You remain amazing, bud.

[Weston Bye]

I wonder how it's going to hold up to heavy loading like knurling. Guess I'll give it a try, too.

I just returned from a visit to a molded gear manufacturer near Chicago.

http://www.winzelergear.com/

They do nothing but design and mold gears from acetal, specifically DuPont Delrin. (uniform quality, superior performance) Quite an eduaction.

To address the above question, they showed us that while a normal gear of any material should exhibit at least one point of contact or a little more, a Delrin gear under load may safely deform the teeth enough to achieve up to four points of contact with a similar mating gear. The additional points of contact then share the load. Such is not the case with a metal gear as the teeth cannot flex as much.

Similarly, in the case of the leadscrew nut, the acetel threads can flex a little to conform to the leadscrew to share the loading.

[Greg Q]

Evan, thanks for taking the time to post your brainstorm results.

I'll be making an EvaNut™ for my lathe next week.

Greg

[Evan]

Hey, I like it! I was trying to think of a name for it. It is officially the EvaNut®.

I knew it was going to be easy to make when it worked so well on the first try. Now that it has been sucessfully replicated on opposite sides of the planet there should be no reason why it cannot be made anywhere in between. Thank you all for the nice words people. I really needed something positive in my life right now.

[EVguru]

they showed us that while a normal gear of any material should exhibit at least one point of contact or a little more, a Delrin gear under load may safely deform the teeth enough to achieve up to four points of contact with a similar mating gear. The additional points of contact then share the load. Such is not the case with a metal gear as the teeth cannot flex as much.

That was the idea behind plastic rear sprockets for motorcycles. It was used successfully on the Laerverda Tripples in endurance racing and was show to greatly increase chain life on the road.

Unfortunately, many people neglect their chains and as soon as they start generating heat, the sprocket starts melting.

They're still used in Karting.

[mochinist]

That's is pretty damn cool, excellent contribution.